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and historical documentation (Appendix E). An additional purpose is to obtain data sufficient to augment the existing Site conceptual model (CSM). 1.3 Site Characterization Objectives The proposed objectives of the characterization of soil, soil gas, and groundwater sampling are listed below. • Indoor air sampling as part of a vapor intrusion assessment of the Quality Cleaners and adjacent tenant suites, specifically, the Comcast store to the east and the Fred Loya Insurance office to the west, respectively. This task is necessary given that a December 2014 sub-slab soil gas sample contained 350 micrograms per cubic meter (µg/m3) of trichloroethene (TCE), a concentration that may, if vapor intrusion has occurred, exceed the DTSC's indoor air Commercial/Industrial Accelerated Response Action Level of 8 µg/m3 as promulgated in the DTSC's August 23, 2014 Human and Ecological Risk Office (HERO) Human Health Risk Assessment (HHRA)Note Number 5. • Sub-slab soil gas sampling beneath the Quality Cleaners as part of a vapor intrusion assessment of the Quality Cleaners. A single five-foot deep soil gas probe will also be installed beneath the dry cleaners suite to assess the vertical extent and attenuation of PCE and other potential volatile organic compounds (VOCs). A December 2014 sub-slab soil gas sample beneath the Quality Cleaners suite contained 3,300 µg/m3 of PCE and 350 µg/m3 of TCE and a groundwater sample southwest and proximate to the Quality Cleaners contained 30 micrograms per liter(µg/L) of PCE. • Shallow soil gas sampling from five-foot deep soil gas probes along the southern boundary of the Site to assess the potential for vapor intrusion related to the residential structures located approximately 100 feet south of the Quality Cleaners. Soil gas sampling from six soil gas probes installed along the alignment of an approximately 660-foot long sewer lateral associated with the Quality Cleaners to assess whether a significant release of PCE has occurred from the sewer lateral. • Installing and monitoring of groundwater monitoring wells in the presumed upgradient and downgradient locations relative to the Quality Cleaners to define the potential lateral extent of PCE and other VOCs in groundwater and to verify the groundwater flow direction. The vertical characterization will occur following the confirmation of the groundwater flow direction using continuously cored soil borings and the collection of grab groundwater samples from targeted strata. • The historical Documentation from 1991 noted a potential issue with a petroleum hydrocarbon release within the Site boundaries. The DTSC requested soil borings be advanced at a location southwest of the intersection of North Tracy Boulevard and Clover Road and from three additional locations within the Site. Based on the 1991 analysis of Sampling and Analysis Workplan Tracy Corners Shopping Center 3225 North Tracy Boulevard Tracy,California 95376 Partner Project Number SM14-129814 Docket Number HAS-VCA 14/15-108 August 15,2016 Page 2